Hot formed parts with coating-free press hardening steels and method thereof

ABSTRACT

An alloy composition comprises that carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 3% by weight of the alloy composition; silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition; either: chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition; and a balance of the alloy composition being iron. Also discloses an alloy composition and a method of producing a press hardening steel object.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.

Press-hardening steel (PHS), also referred to as “hot-stamped steel” or “hot formed steel,” is one of the strongest steels used for automotive body structural applications, having tensile strength properties on the order of about 1,500 mega-Pascal (MPa). Such steel has desirable properties, including forming steel components with significant increases in strength-to-weight ratios. PHS components have become ever more prevalent in various industries and applications, including general manufacturing, construction equipment, automotive or other transportation industries, home or industrial structures, and the like. For example, when manufacturing vehicles, especially automobiles, continual improvement in fuel efficiency and performance is desirable, thus PHS components have been increasingly used. PHS components are often used for forming load-bearing components, like door beams, which usually require high strength materials. Thus, the finished state of these steels are designed to have high strength and enough ductility to resist external forces, for example, to resist intrusion into the passenger compartment without fracturing so as to provide protection to the occupants. Moreover, galvanized PHS components may provide cathodic protection.

Many PHS processes involve austenitization in a furnace of a sheet steel blank immediately followed by pressing and quenching of the sheet in dies. There are two main types of PHS processes: indirect and direct. Austenitization is typically conducted in the range of about 880° C. to 950° C. Under the direct method, the PHS component is formed and pressed simultaneously between dies, which quenches the steel. Under the indirect method, the PHS component is cold formed to an intermediate partial shape before austenitization and the subsequent pressing and quenching steps. The quenching of the PHS component hardens the component by transforming the microstructure from austenite to martensite. An oxide layer often forms during the transfer from the furnace to the dies. After quenching, therefore, the oxide must be removed from the PHS component and the dies. The oxide is typically removed, i.e., descaled, by shot blasting.

The PHS component may be coated prior to applicable pre-cold forming (if the indirect process is used) or austenitization. Coating the PHS component provides a protective layer (e.g., galvanic protection) to the underlying steel component. Such coatings typically include an aluminum-silicon alloy and/or zinc. Zinc coatings offer cathodic protection; the coating acts as a sacrificial layer and corrodes instead of the steel component, even where the steel is exposed. Such coatings also generate oxides on PHS components' surfaces, which are removed by shot blasting.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

The present disclosure is related to a novel coating-free press hardening steel and method to produce press hardening steel parts. The novel coating-free press hardening steel includes chromium, aluminum, or both chromium and aluminum.

The current technology provides an alloy composition including carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition; manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 3% by weight of the alloy composition; silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition; either chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition; and a balance of the alloy composition being iron.

In various aspects, the alloy composition is a high Cr alloy composition that includes chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition.

In various aspects, the high Cr alloy composition includes aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition.

In various aspects, the high Cr alloy composition has been oxidized at a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 60 minutes and then cooled.

In various aspects, the high Cr alloy composition is configured to be hardened into a press hardening steel by subjecting the high Cr alloy composition to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. form a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes and then cooling.

In various aspects, the high Cr alloy composition does not require shot blasting after being used for hot forming.

In various aspects, the high Cr alloy composition is a in the form of a sheet and at least one surface of the sheet comprises a layer of Cr-enriched oxide. In some aspects, the layer of Cr-enriched oxide has a thickness of from greater than or equal to about 1 μm to less than or equal to about 40 μm.

In various aspects, the alloy composition is a high Al alloy composition that includes aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 6% by weight of the alloy composition.

In various aspects, the high Al alloy composition includes chromium at a concentration of from greater than or equal to about 0.05% by weight to less than or equal to about 0.3% by weight of the alloy composition. In some aspects, the high Al alloy composition includes aluminum at a concentration of about 4% by weight of the alloy composition.

In various aspects, the high Al alloy composition has a density that is 5% less than a second alloy composition having the same components, but with an aluminum concentration of less than or equal to about 0.05% by weight of the second alloy composition.

In various aspects, the high Al alloy composition is configured to be hardened into a press hardening steel by subjecting the alloy composition to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. form a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes and then cooled. In some aspects, the press hardening steel has a predetermined shape and at least one surface of the predetermined shape comprises a layer of Al-enriched oxide. In other aspects, the press hardening steel does not require shot blasting after being used for hot forming.

The current technology also provides an alloy composition including carbon at a concentration of from greater than or equal to about 0.2% by weight to less than or equal to about 0.3% by weight of the alloy composition; boron at a concentration of from greater than or equal to about 0.001% by weight to less than or equal to about 0.005% by weight of the alloy composition; manganese at a concentration of from greater than or equal to about 0.5% by weight to less than or equal to about 3% by weight of the alloy composition; silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition; either chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0.02% by weight to less than or equal to about 5% by weight of the alloy composition, or aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 5% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition; and a balance of the alloy composition being iron.

The current technology also provides a method of producing a press hardening steel object. The method includes heating an alloy blank to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes to generated a heated alloy blank. The alloy blank is composed of an alloy composition including carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 3% by weight of the alloy composition; silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition; chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, and a balance of the alloy composition being iron. The method also includes transferring the heated alloy blank to a die to form the heated alloy blank into an object with a predetermined shape, and quenching the object with a predetermined shape to generate an object composed of press hardening steel. The press hardening steel object has at least one surface comprising an oxide layer. The method does not require shot blasting.

In various aspects, the quenching the object includes cooling the object at a rate of greater than or equal to about 15° C./s.

In various aspects, the alloy composition includes chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition, and the method further comprises, prior to the heating, pre-oxidizing the alloy composition by heating the alloy composition to a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 60 minutes and then cooling the alloy composition.

In various aspects, the alloy composition includes aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition, and the method further includes, prior to the quenching, soaking the heated alloy blank at a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. in the presence of niobium and vanadium.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1A is a micrograph of a surface of a press hardening steel made from a high Cr alloy composition that was not pre-oxidized;

FIG. 1B is a micrograph of a surface of a press hardening steel made from a high Cr alloy composition that was pre-oxidized;

FIG. 2A is a micrograph showing the surface of a steel with 3% Cr by weight made by heating a steel with 3% Cr by weight composition to 900° C. for 10 minutes and cooling;

FIG. 2B is a micrograph showing the surface of a steel with 9% Cr by weight made by heating a steel with 9% Cr by weight composition to 900° C. for 10 minutes and cooling;

FIG. 3A is a micrograph showing the surface of a steel with 3% Cr by weight made by heating a steel with 3% Cr by weight composition to 500° C. for 20 minutes and cooling;

FIG. 3B is a micrograph showing the surface of a steel with 9% Cr by weight made by heating a 9% steel with 9% Cr by weight composition to 600° C. for 10 minutes and cooling;

FIG. 4A is a micrograph showing the surface of a steel with 3% Cr by weight made by heating a steel with 3% Cr by weight composition to 500° C. for 20 minutes and cooling followed by heating to 900° C. for 10 minutes and cooling;

FIG. 4B is a micrograph showing the surface of a steel with 9% Cr by weight made by heating a steel with 9% Cr by weight composition to 600° C. for 10 minutes and cooling followed by heating to 900° C. for 10 minutes and cooling;

FIG. 5A is a first micrograph showing the thickness of a Cr-enriched oxide layer that formed on a high Cr alloy composition after pre-oxidizing by heating at 500° C. for 20 minutes and cooling, and hardening by heating at 900° C. for 10 minutes followed by cooling;

FIG. 5B is a second micrograph showing the thickness of a Cr-enriched oxide layer that formed on a high Cr alloy composition after pre-oxidizing by heating at 500° C. for 20 minutes and cooling, and hardening by heating at 900° C. for 10 minutes followed by cooling;

FIG. 6A is a photograph showing the surface of bare 22MnB5 steel heated at 900° C. for 6 minutes and hot stamped;

FIG. 6B is a photograph showing the surface of AlSi-coated 22MnB5 steel after hot stamping;

FIG. 6C is a photograph showing the surface of Zn-coated steel after hot stamping;

FIG. 6D is a photograph of a surface of uncoated/bare steel with 3% Cr by weight that was pre-oxidized by heating at 500° C. for 20 minutes and cooling, and hardened by heating at 900° C. for 10 minutes followed by cooling;

FIG. 6E is a photograph of a surface of uncoated/bare steel with 9% Cr by weight that was pre-oxidized by heating at 600° C. for 10 minutes and cooling, and hardened by heating at 900° C. for 10 minutes followed by cooling;

FIG. 7 is a graph showing the thermodynamics of a 0.22% C-1.5% Mn+XCr (by weight) system, wherein the x-axis is chromium concentration (wt. %) and the y-axis is temperature (° C.);

FIG. 8 is a graph showing the kinetics of a 0.22% C-1.5% Mn+XCr (by weight) system, wherein the x-axis is time and the y-axis is temperature;

FIG. 9 is a flowchart showing a method for preparing a press-hardened steel object;

FIG. 10A is a micrograph at a first magnification of high Al hardened steel;

FIG. 10B is a micrograph at a second magnification of the high Al hardened steel shown in FIG. 10A;

FIG. 11A is a photograph showing the surface of bare 22MnB5 steel heated at 900° C. for 6 minutes and hot stamped;

FIG. 11B is a photograph showing the surface of AlSi-coated 22MnB5 steel after hot stamping;

FIG. 11C is a photograph showing the surface of Zn-coated steel;

FIG. 11D is a photograph of a surface of uncoated/bare high Al steel that was hardened by heating at 900° C. for 10 minutes followed by cooling; and

FIG. 11E is a photograph of a surface of uncoated/bare high Al steel that was hardened by heating at 1000° C. for 3 minutes followed by cooling.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of.” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.

Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.

When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.

Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.

Example embodiments will now be described more fully with reference to the accompanying drawings.

Alloy Compositions

The current technology provides an alloy composition that is configured to form a protective oxide layer before and/or during hot stamping processes. The alloy composition has at least one of high chromium content or high aluminum content and does not require coatings, which can be expensive, or shot blasting to remove scale, which is time consuming and requires additions cost. In various aspects, an alloy composition having a high chromium content can be oxidized prior to and during hot stamping. In various other aspects, an alloy composition having high aluminum content is lower weight than another alloy composition having the same components, but without the high aluminum content.

In various aspects of the current technology, the alloy composition is in the form of a blank for hot stamping processes. Accordingly, the blank forms a press hardening steel after hot stamping processes. Components within alloy composition, such as, for example, boron and chromium, lower a critical cooling rate in hot stamping processes relative to critical cooling rates employed without such components.

The alloy composition comprises carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, greater than or equal to about 0.15% by weight to less than or equal to about 0.4% by weight of the alloy composition, greater than or equal to about 0.15% by weight to less than or equal to about 0.3% by weight of the alloy composition, greater than or equal to about 0.15% by weight to less than or equal to about 0.25% by weight of the alloy composition, or greater than or equal to about 0.15% by weight to less than or equal to about 0.2% by weight of the alloy composition.

The alloy composition also comprises chromium and aluminum, wherein the alloy composition has either high chromium content and relatively low aluminum content or high aluminum content and relatively low chromium content.

In various aspects, a balance of the alloy composition is iron.

When the alloy composition has a high chromium content, i.e., when the composition is a high chromium (Cr) alloy composition, the chromium is included at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition, from greater than or equal to about 2% by weight to less than or equal to about 8% by weight of the alloy composition, from greater than or equal to about 2% by weight to less than or equal to about 6% by weight of the alloy composition, from greater than or equal to about 2% by weight to less than or equal to about 4% by weight of the alloy composition, or about 3% by weight of the alloy composition, and the aluminum is included at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, from greater than or equal to about 0.1% by weight to less than or equal to about 4.5% by weight of the alloy composition, from greater than or equal to about 1% by weight to less than or equal to about 4% by weight of the alloy composition, from greater than or equal to about 2% by weight to less than or equal to about 3% by weight of the alloy composition, from greater than or equal to about 0% by weight to less than or equal to about 0.1% by weight of the alloy composition, from greater than or equal to about 0.015% by weight to less than or equal to about 0.075% by weight of the alloy composition, or from greater than or equal to about 0.02% by weight to less than or equal to about 0.05% by weight of the alloy composition. In the high chromium alloy composition, the carbon concentration is from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, or from greater than or equal to about 0.2% by weight to less than or equal to about 0.3% by weight of the alloy composition.

When the alloy composition has a high aluminum content, i.e., when the composition is a high aluminum (Al) alloy composition, the aluminum is included at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition, from greater than or equal to about 3% by weight to less than or equal to about 8% by weight of the alloy composition, from greater than or equal to about 3.5% by weight to less than or equal to about 6% by weight of the alloy composition, from greater than or equal to about 4% by weight to less than or equal to about 5% by weight of the alloy composition, or about 4% by weight of the alloy composition, and the chromium is included at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, from greater than or equal to about 0.1% by weight to less than or equal to about 4.5% by weight of the alloy composition, from greater than or equal to about 1% by weight to less than or equal to about 4% by weight of the alloy composition, from greater than or equal to about 2% by weight to less than or equal to about 3% by weight of the alloy composition, from greater than or equal to about 0.075% by weight to less than or equal to about 0.25% by weight of the alloy composition, or from greater than or equal to about 0.1% by weight to less than or equal to about 0.2% by weight of the alloy composition. In the high aluminum alloy composition, the carbon concentration is from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% of the alloy composition, from greater than or equal to about 0.2% by weight to less than or equal to about 0.5% by weight of the alloy composition, from greater than or equal to about 0.3% by weight to less than or equal to about 0.5% by weight of the alloy composition, or about 0.4% by weight of the alloy composition.

In various aspects of the current technology, the alloy composition also includes boron at a concentration of from greater than or equal to about 0.001% by weight to less than or equal to about 0.005% by weight of the alloy composition, manganese at a concentration of from greater than or equal to about 0.5% by weight to less than or equal to about 3% by weight of the alloy composition, silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition, titanium at a concentration of from greater than or equal to about 0.001% by weight to less than or equal to about 0.1% by weight of the alloy composition, or a combination thereof.

In other aspects, the alloy composition also includes molybdenum, nickel, or a combination thereof at a concentration of from greater than 0% by weight to less than or equal to about 0.2% by weight of the alloy composition, or from greater than 0% by weight to less than or equal to about 0.1% by weight of the alloy composition.

High Cr Alloy Composition

In regard to the high Cr alloy composition, in various aspects it is configured to be pre-oxidized and cooled to generate a pre-oxidized high Cr alloy composition. Pre-oxidizing is performed at a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C., such as a temperature of about 400° C., about 450° C., of about 500° C., about 550° C., about 600° C., about 650° C., or about 700° C. for a time of from greater than or equal to about 1 minute to less than or equal to about 60 minutes, such as time of about 5 minutes, about 10 minutes, about 15 minutes, about 20 minutes, about 25 minutes, about 30 minutes, about 35 minutes, about 40 minutes, about 45 minutes, about 50 minutes about 55 minutes, or about 60 minutes. Cooling is performed by air cooling, water cooling, oil cooling, or in die cooling, as non-limiting examples. The pre-oxidized high Cr alloy composition can be rolled into a coil or provided as a sheet and stored for future use.

The pre-oxidized high Cr alloy composition is configured to be press hardened at a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C., such as a temperature of about 850° C., about 900° C., about 950° C., about 1000° C., or about 1050° C. for a time of from greater than or equal to about 1 minute to less than or equal to about 15 minutes, such as time of about 1 minutes, about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 6 minutes, about 7 minutes, about 8 minutes, about 9 minutes, about 10 minutes, about 11 minutes, about 12 minutes, about 13 minutes, about 14 minutes, or about 15 minutes, followed by cooling, such as, for example, by air cooling, water cooling, oil cooling, or in die cooling.

FIG. 1A shows a micrograph of a surface of a press hardening steel made from a high Cr alloy composition containing 3% Cr by weight of the composition according to the present technology. Here, the high Cr alloy composition is not pre-oxidized. Rather, the high Cr alloy composition is heated to 900° C. for 10 minutes and transferred to water or oil cooled die for press forming and quenching. FIG. 1B shows a second micrograph of a surface of a press hardening steel made from a high Cr alloy composition containing 3% Cr by weight of the composition. Here, the high Cr alloy composition is pre-oxidized at 500° C. for 20 minutes, cooled, and then press hardened at 900° C. for 10 minutes, and then cooled. As can be determined from the micrographs, the press hardening steel of FIG. 1B, which was pre-oxidized, has a superior surface quality relative to the press hardening steel of FIG. 1A, which was not pre-oxidized.

FIG. 2A is a micrograph showing the surface of a steel with 3% Cr by weight and FIG. 2B is a micrograph showing the surface of a steel with 9% Cr by weight. These steels were made without shot blasting. In FIGS. 2A and 2B, the steels were heating at 900° C. for 10 minutes and then cooled. FIG. 3A is a micrograph showing the surface of a steel with 3% Cr by weight and FIG. 3B is a micrograph showing the surface of a steel with 9% Cr by weight. In FIGS. 3A and 3B, the steels were pre-oxidized by heating at 500° C. for 20 minutes and 600° C. for 10 minutes, respectively, and then cooled. FIG. 4A is a micrograph showing the surface of a steel with 3% Cr by weight and FIG. 4B is a micrograph showing the surface of a steel with 9% Cr by weight. In FIGS. 4A and 4B, the steels were pre-oxidized by heating at 500° C. for 20 minutes and 600° C. for 10 minutes, respectively, and cooling and then hardened by heating at 900° C. for 10 minutes followed by cooling. The micrographs of FIGS. 2A, 2B, 3A, 3B, 4A, and 4B show that the best surfaces are those that result from pre-oxidizing prior to hardening. Moreover, when performed in a die during hot stamping, the cooling rate will be much quicker than air cooling, which will generate even better surface quality.

Heat treating the high Cr alloy composition after pre-oxidation results in the formation of a Cr-enriched oxide layer on the hardened high Cr alloy composition. A Cr-enriched oxide layer is a layer having Cr and O or Cr, O, and Fe. In various aspects, the Cr, O, and optional Fe are present as, for example, CrFeO, CrO, Cr₂O₃, CrO₂, CrO₃, CrO₅, or Cr₈O₂. The Cr-enriched oxide layer has a thickness of from greater than or equal to about 1 μm to less than or equal to about 40 μm. FIGS. 5A and 5B are micrographs that show the thickness of a Cr-enriched oxide layer that formed on a high Cr alloy composition after pre-oxidizing by heating at 500° C. for 20 minutes and cooling, and hardening by heating at 900° C. for 10 minutes followed by cooling. The average thickness of the Cr-enriched oxide layers is about 10 μm.

FIG. 6A is a photograph showing the surface of bare 22MnB5 steel heated at 900° C. for 6 minutes and hot stamped. FIGS. 6B and 6C show photographs of surfaces of AlSi-coated 22MnB5 steel and Zn-coated steel after hot stamping. FIGS. 6D and 6E show photographs of surfaces of uncoated/bare steel with 3% Cr by weight and uncoated/bare steel with 9% Cr by weight, respectively, wherein the steel with 3% Cr by weight is pre-oxidized by heating at 500° C. for 20 minutes and cooling, and hardened by heating at 900° C. for 10 minutes followed by cooling. The steels according to the present technology shown in FIGS. 6D and 6E have a significantly better surface quality than the bare 22MnB5 steel shown in FIG. 6A. Moreover, the steels according to the present technology shown in FIGS. 6D and 6E have comparable surface quality relative to the coated steels shown in FIGS. 6B and 6C.

Hardened steel made from the high Cr alloy composition has an ultimate tensile strength (UTS) of greater than or equal to about 1200 MPa, such as a UTS of about 1200 MPa, about 1250 MPa, about 1300 MPa, about 1350 MPa, about 1400 MPa, about 1450 MPa, about 1500 MPa, about 1550 MPa, about 1600 MPa, about 1650 MPa, about 1700 MPa, about 1750 MPa, about 1800 MPa, about 1850 MPa, about 1900 MPa, about 1950 MPa, about 2000 MPa, or greater. Also, the hardened steel made from the high Cr alloy composition has a ductility (elongation) of greater than or equal to about 4% (elongation) to less than or equal to about 10% (elongation), such as a ductility of about 4% (elongation), about 5% (elongation), about 6% (elongation), about 7% (elongation), about 8% (elongation), about 9% (elongation), or about 10% (elongation) in the hardened condition.

Table 1 shows various exemplary characteristics of 22MnB5 and of 2.25-5Cr according to the current technology. This table is provided for comparison purposes and may not reflect all the acceptable characteristic ranges for the 2.25%-5% Cr alloy provided herein.

TABLE 1 Process Parameters For High Cr Alloy Compositions Forming & Alloy Composition Soaking Quenching Property Coating 22MnB5 0.22% C—1.5% 900° C. >30° C./s 1500 MPa bare or Mn cooling 6% EL AlSi everywhere coated High Cr 0.22% C—2.25-5% 500° C. for >15° C./s 1600 MPa no alloy Cr—Mn—Si 20 min + cooling 6% EL coating 900° C. for everywhere 10 min

Without being bound by theory, adding high levels of Cr to the alloy composition, such as, for example, about 3% Cr by weight of the composition decreases the austenitization temperature. FIG. 7 shows a thermodynamics graph, wherein the x-axis 10 represents Cr concentration for a 0.22% C-1.5% Mn+xCr steel and the y-axis 12 represents temperature in ° C. A first region 14 is shown for body-centered cubic (bcc)+face-centered cubic (fcc) 0.22% C-1.5% Mn+xCr steel, a second region 16 is shown for bcc+M₇C₃ (carbide) steel, a third region 18 is shown for bcc+fcc+M₇C₃ (carbide) steel, a fourth region 20 is shown for fcc+M₇C₃ (carbide) steel, and a fifth region 22 is shown for bcc+M₂₃C₆ (carbide) steel. A baseline temperature 24 is shown at about 800° C. and a hot stamping area 26 is shown for 0.22% C-1.5% Mn+xCr. According to the graph, including Cr at a concentration of about 3% by weight of the alloy composition lowers the temperature required for hot stamping from the baseline temperature 24 of about 800° C. to an fcc point 28 of about 780° C.

Also without being bound by theory, adding high levels of Cr to the alloy composition, such as, for example, about 3% Cr by weight of the composition, increases the time required for the critical cooling rate which broadens the processes time window. A cooling rate in a die is greater than 15° C./s and a baseline rate is greater than 30° C./s. FIG. 8 shows a kinetics graph, wherein the x-axis 30 represents time and the y-axis 32 represents temperature. An A3 (α-ferrite or bcc ferrite) baseline temperature 34, an M_(s) (martensite begins to form) baseline temperature 36, and an M_(f) (martensite formation completes) baseline temperature 38 are shown in the y-axis 32. A first curve 40 representing the critical cooling rate of a steel, a second curve 42 representing ferrite, a third curve 44 representing pearlite, and a fourth curve 46 for bainitic transformation is shown on the graph. By adding Cr to the composition at a concentration of 3% by weight of the composition, the critical cooling rate slides toward the right side of the graph as represented by the dotted curves 40′, 42′, 44′, 46′, which correspond to the first, second, third, and fourth curves 40, 42, 44, 46 respectively. This increase in critical cooling rate provides a broader process window.

Accordingly, in various aspect, the high Cr alloy composition is configured to be quenched, i.e., cooled, at a rate of greater than or equal to about 15° C./s, greater than or equal to about 20° C./s, or greater than or equal to about 25° C./s.

Any alloy composition known in the art can be modified by including the above described chromium content in order to impart the advantageous characteristics provided by the chromium. Non-limiting examples of such alloy compositions include 22Mn, 22MnB5, 25MnB5, 30MnB5, 22MnB5+Nb/V, 25MnB5+Nb/V, and 30MnB5+Nb/V.

The current technology also provides a method of producing a press hardened high Cr steel object. The steel object can be any object that is generally made by hot stamping, such as, for example, vehicle parts. Non-limiting examples of vehicles that have parts suitable to be produced by the current method include bicycles, automobiles, motorcycles, boats, tractors, buses, mobile homes, campers, gliders, airplanes, and tanks. The method comprises heating an alloy blank to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes to generated a heated alloy blank. The blank is a high Cr alloy composition as described above. For example, the blank is composed of an alloy composition comprising carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition, and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition.

In some aspects, the blank is provided as a pre-oxidized sheet, roll, or coil of the high Cr alloy composition. In other aspects, the blank is not pre-oxidized and the method includes, prior to the hot forming process, pre-oxidizing the high Cr alloy composition by heating the high Cr alloy composition to a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 60 minutes and then cooling the alloy composition.

After pre-oxidation and heating the blank to austenitization temperature, the method comprises transferring the heated alloy blank to a die to form the heated alloy blank into an object with a predetermined shape, and quenching the object to generate an object composed of high Cr press hardening steel. Quenching the object comprises cooling the object at a rate of greater than or equal to about 15° C./s. The press hardening steel object has at least one surface comprising a layer of Cr-enriched oxide. Shot blasting is not required after hot forming in the method. However, the method optionally includes trimming the object composed of high Cr press hardening steel, such as, for example, by laser trimming.

FIG. 9 is a flow chart that provides an exemplary method 50 of producing a press hardening steel object. Here the method includes obtaining a blank 52 composed of a high Cr alloy composition, cutting the blank 52 into sheets 54 having a size that roughly corresponds to the size of the press hardening steel object, and forming a press hardening steel object 56 by hot stamping. In various aspects, the blank 52 is pre-oxidized or not pre-oxidized. When the blank 52 is not pre-oxidized, the method includes pre-oxidizing the blank or the sheet 54 by heating to a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 60 minutes and then cooling the high Cr alloy composition. Hot stamping comprises heating the sheet 54 to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes and transferring the heated sheet 54 to a die. After quenching, as described above, the press hardening steel object 56 is removed from the die.

High Al Alloy Composition

In regard to the high Al alloy composition, it has a density that is 5% less than a second alloy composition having the same components, but with an aluminum concentration of less than or equal to about 0.05% by weight of the second alloy composition. For example, adding 4% by weight Al in steel can lead to a 5% weight reduction. Also, the high Al alloy composition can be rolled into a coil or provided as a sheet.

The high Al alloy composition is configured to be press hardened at a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C., such as a temperature of about 850° C., about 900° C., about 950° C., about 1000° C., or about 1050° C. for a time of from greater than or equal to about 1 minute to less than or equal to about 15 minutes, such as time of about 1 minutes, about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 6 minutes, about 7 minutes, about 8 minutes, about 9 minutes, about 10 minutes, about 11 minutes, about 12 minutes, about 13 minutes, about 14 minutes, or about 15 minutes, followed by cooling. Cooling is performed by air cooling, water cooling, oil cooling, or in die cooling, as non-limiting examples. In various aspects, the heating includes soaking in the presence of at least one of niobium and vanadium, the niobium concentration being from greater than or equal to about 0.01% by weight to less than or equal to about 0.1% by weight of the alloy composition and the vanadium concentration being from greater than or equal to about 0.05% by weight to less than or equal to about 0.5% by weight of the alloy composition. In one embodiment, soaking occurs in the presence of about 0.05% by weight niobium and 0.2% by weight vanadium. The hardened high Al alloy has at least one surface comprising an Al-enriched oxide layer. An Al-enriched oxide layer is a layer having Al and O or Al, O, and Fe. In various aspects, the Al, O, and optional Fe are present as, for example, AlFeO, AlO, Al₂O, or Al₂O₃. The Al-enriched oxide layer has a thickness of from greater than or equal to about 1 μm to less than or equal to about 40 μm.

FIGS. 10A and 10B are micrographs at different magnifications of high Al hardened steel made from the high Al alloy composition. In particular, the high Al hardened steel is generated from a Fe-3˜5% Al—C—Mn alloy composition according to the current technology. The alloy composition is heated at 900° C. for about 10 minutes and then cooled to generate the hardened steel. The hardened steel has good surface quality.

FIG. 11A is a photograph showing the surface of bare 22MnB5 steel heated at 900° C. for 6 minutes. FIGS. 11B and 2C show photographs of surfaces of AlSi-coated 22MnB5 steel and Zn-coated steel after hot stamping. FIGS. 11D and 11E show photographs of surfaces of uncoated/bare Fe-3˜5% Al—C—Mn steel hardened at 900° C. for 10 minutes and at 1000° C. for 3 minutes, respectively. The steels according to the present technology shown in FIGS. 11D and 12E have a significantly better surface quality than the bare 22MnB5 steel shown in FIG. 11A. Moreover, the steels according to the present technology shown in FIGS. 11D and 11E have comparable surface quality relative to the coated steels shown in FIGS. 11B and 11C.

Hardened steel made from the high Al alloy composition has an ultimate tensile strength (UTS) of greater than or equal to about 1100 MPa, such as a UTS of about 1100 MPa, about 1150 MPa, about 1200 MPa, about 1250 MPa, about 1300 MPa, about 1350 MPa, about 1400 MPa, about 1450 MPa, about 1500 MPa, about 1550 MPa, about 1600 MPa, about 1650 MPa, about 1700 MPa, about 1750 MPa, about 1800 MPa or greater. Also, the hardened steel made from the high Al alloy composition has a ductility (elongation) of greater than or equal to about 4% (elongation) to less than or equal to about 20% (elongation), such as a ductility of about 4% (elongation), about 5% (elongation), about 6% (elongation), about 7% (elongation), about 8% (elongation), about 9% (elongation), about 10% (elongation), about 12% (elongation), about 14% (elongation), about 16% (elongation), about 18% (elongation), or about 20% (elongation), in the hardened condition.

Table 2 shows various exemplary characteristics of 22MnB5 and of high Al steel according to the current technology. This table is provided for comparison purposes and may not reflect all the acceptable characteristic ranges for the high Al steel alloy provided herein.

TABLE 2 Process Parameters For High Al Alloy Compositions Forming & Alloy Composition Soaking Quenching Property Coating 22MnB5 0.22% C 900° C. >30° C./s 1500 MPa bare or 1.5% Mn—Si cooling 6% EL AlSi everywhere coated high Al 0.4% C 880° C.-1000° C. >15° C./s 1400 MPa no steel 3.5% Al—Mn—Si with cooling 10% EL coating Nb/V everywhere

In various aspect, the high Al alloy composition is configured to be quenched, i.e., cooled, at a rate of greater than or equal to about 15° C./s, greater than or equal to about 20° C./s, or greater than or equal to about 25° C./s.

Any alloy composition known in the art can be modified by including the above described aluminum content in order to impart the advantageous characteristics provided by the aluminum. Non-limiting examples of such alloy compositions include 22Mn, 22MnB5, 25MnB5, 30MnB5, 22MnB5+Nb/V. 25MnB5+Nb/V, 30MnB5+Nb/V, 35MnB5+Nb/V.

The current technology also provides a method of producing a press hardened high Al steel object. The steel object can be any object that is generally made by hot stamping, such as, for example, vehicle parts. Non-limiting examples of vehicles that have parts suitable to be produced by the current method include bicycles, automobiles, motorcycles, boats, tractors, buses, mobile homes, campers, gliders, airplanes, and tanks. The method comprises heating an alloy blank to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes to generated a heated alloy blank. The blank is a high Al alloy composition as described above. For example, the blank is composed of an alloy composition comprising carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.3% by weight of the alloy composition, silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition, aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition, chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, and a balance of the alloy composition being iron. The blank is provided as a sheet, roll, or coil of the high Al alloy composition.

After the heating, the method comprises transferring the heated alloy blank to a die to form the heated alloy blank into an object with a predetermined shape, and quenching the object to generate an object composed of high Al press hardening steel. Quenching the object comprises cooling the object at a rate of greater than or equal to about 15° C./s. The press hardening steel object has at least one surface comprising a layer of Al-enriched oxide. Shot blasting is not required in the method. However, the method optionally includes trimming the object composed of high Al press hardening steel, such as, for example, by laser trimming.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. An alloy composition comprising: carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition; manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 3% by weight of the alloy composition; silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition; either: chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition; and a balance of the alloy composition being iron.
 2. The alloy composition according to claim 1, comprising chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition.
 3. The alloy composition according to claim 2, comprising aluminum at a concentration of from greater than or equal to about 0.02% by weight to less than or equal to about 0.05% by weight of the alloy composition.
 4. The alloy composition according to claim 2, wherein the alloy composition has been oxidized at a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 60 minutes and then cooled.
 5. The alloy composition according to claim 2, wherein the alloy composition is configured to be hardened into a press hardening steel by subjecting the alloy composition to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. form a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes and then cooled.
 6. The alloy composition according to claim 5, wherein the press hardening steel does not require shot blasting after being used for hot forming.
 7. The alloy composition according to claim 2, wherein the alloy composition is in the form of a sheet and at least one surface of the sheet comprises a layer of Cr-enriched oxide.
 8. The alloy composition according to claim 7, wherein the layer of Cr-enriched oxide has a thickness of from greater than or equal to about 1 μm to less than or equal to about 40 μm.
 9. The alloy composition according to claim 1, comprising aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 6% by weight of the alloy composition.
 10. The alloy composition according to claim 9, comprising chromium at a concentration of from greater than or equal to about 0.05% by weight to less than or equal to about 0.3% by weight of the alloy composition.
 11. The alloy composition according to claim 10, wherein the aluminum has a concentration of about 4% by weight of the alloy composition.
 12. The alloy composition according to claim 9, wherein the alloy composition has a density that is 5% less than a second alloy composition having the same components, but with an aluminum concentration of less than or equal to about 0.05% by weight of the second alloy composition.
 13. The alloy composition according to claim 9, wherein the alloy composition is configured to be hardened into a press hardening steel by subjecting the alloy composition to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. form a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes and then cooled.
 14. The alloy composition according to claim 13, wherein the press hardening steel has a predetermined shape and at least one surface of the predetermined shape comprises a layer of Al-enriched oxide.
 15. The alloy composition according to claim 14, wherein the press hardening steel does not require shot blasting after being used for hot forming.
 16. An alloy composition comprising: carbon at a concentration of from greater than or equal to about 0.2% by weight to less than or equal to about 0.3% by weight of the alloy composition; boron at a concentration of from greater than or equal to about 0.001% by weight to less than or equal to about 0.005% by weight of the alloy composition; manganese at a concentration of from greater than or equal to about 0.5% by weight to less than or equal to about 3% by weight of the alloy composition; silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition; either: chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 5% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition; and a balance of the alloy composition being iron.
 17. A method of producing a press hardening steel object, the method comprising: heating an alloy blank to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes to generated a heated alloy blank, wherein the alloy blank is composed of an alloy composition comprising: carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 3% by weight of the alloy composition, silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition, either: chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, and a balance of the alloy composition being iron; transferring the heated alloy blank to a die to form the heated alloy blank into an object with a predetermined shape; and quenching the object with a predetermined shape to generate an object composed of press hardening steel, wherein the press hardening steel object has at least one surface comprising an oxide layer and wherein the method does not require shot blasting.
 18. The method according to claim 17, wherein the quenching the object comprises cooling the object at a rate of greater than or equal to about 15° C./s.
 19. The method according to claim 17, wherein the alloy composition comprises chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition, and the method further comprises, prior to the heating: pre-oxidizing the alloy composition by heating the alloy composition to a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 60 minutes and then cooling the alloy composition.
 20. The method according to claim 17, wherein the alloy composition comprises aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition, and the method further comprises, prior to the quenching: soaking the heated alloy blank at a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. in the presence of niobium and vanadium. 